It’s just what the law is, as developed over centuries going back to English common law.
Under this legal doctrine, even though it is later discovered that a government official who holds color of official title to his office by virtue of a known election or appointment failed to meet a prerequisite of holding office, such as an eligibility requirement, nevertheless actions taken by him within the scope and by the apparent authority of that office will be considered valid and binding.
There is an argument to be made under the language in the cases that once the citizenry is on notice of the defect in the office-holder, that they are not entitled to rely on official acts and from that point on the acts should be considered void.
However, because the MSM has ignored or ridiculed this at least as of now I would not say that the citizenry at large is as aware of this, as say, the TomKat divorce, so I don’t think we are yet in a position to apply that aspect of the case law.
baloney de facto officer doctrine does not apply obama was challenged before he took office..keep reading case law
Correct me if I'm wrong, but I think Clean Hands Doctrine would also be in play, would it not? The De Facto Officer Doctrine exists to protect those who were innocent of the deception from unjust harm that would have befall them if the officer's actions were voided, but the Clean Hands Doctrine would imply that those who were in any way a party to the deception would not be entitled to such protection.
That would have to ignore the fact that many of those actions taken unilaterally by the Executive Branch per his orders were beyond the limits of Constitutional power. Those edicts, appointments, etc. could well be void because there is no way to make the case that they were done with the approval of the Legislative Branch, something which could be done with legislation passed first by the Congress.